The present invention relates to an amplitude equalizer for use in a signal transmission system.
A signal transmission system requires amplitude equalization to realize desired transmission characteristics. One such equalizer, the transversal filter described in "Principles of Data Communications," MacGraw-Hill, 1968, Chapter 6, is well known. This filter comprises a plurality of delay lines and means for synthesizing a signal from each tap of the delay lines with predetermined weighting. The equalizer of this type, however, has drawbacks in that (i) the required circuit network becomes enormous as the number of taps increases since the gain of each tap must be controlled, and (ii) the delay time in each delay line should be selected to be equal to the inverse of the data transmission rate. This equalizer, therefore, could not be utilized in a system where transmission rate is close to the inverse number of the delay time and is thus of limited use.
An improved equalizer has been also proposed in a co-pending U.S. patent application Ser. No. 29,503, filed on Apr. 12, 1979 now U.S. Pat. No. 4,258,340, by the same assignee as the present application. The amplitude equalizer described therein includes a phase shift circuit and two variable attenuators.